Limited availability of l-arginine increases DNA-binding activity of NF-κB and contributes to regulation of iNOS expression

A Tripeptide (Ser-Arg-Pro, SRP) from Sipunculus nudus L. Improves Cadmium-Induced Acute Kidney Injury by Targeting the MAPK, Inflammatory, and Apoptosis Pathways in Mice

Cadmium (Cd) is a toxic heavy metal that causes nephrosis, including acute kidney injury. To prevent and treat acute kidney injury (AKI) following Cd exposure, a tripeptide, Ser-Arg-Pro (SRP), from Sipunculus nudus L. was employed, and its potential efficacy in AKI was assessed. Oral administration of SRP significantly alleviated Cd-induced kidney damage, leading to improved renal function and the attenuation of structural abnormalities. A network pharmacology analysis revealed the potential of SRP in renal protection by targeting various pathways, including mitogen-activated protein kinase (MAPK) signaling, inflammatory response, and apoptosis pathways. Mechanistic studies indicated that SRP achieves renal protection by inhibiting the activation of MAPK pathways (phosphorylation of p38, p56, ERK, and JNK) in the oxidative stress cascade, suppressing inflammatory responses (iNOS, Arg1, Cox2, TNF-α, IL-1β, and IL-6), and restoring altered apoptosis factors (caspase-9, caspase-3, Bax, and Bcl-2). Hence, SRP has the potential to be used as a therapeutic agent for the treatment of Cd-induced nephrotoxicity.

Gastro-protective effect of l-arginine against nitric oxide deficiency-related mucosal injury induced by indomethacin: Does age matter?

Gastric ulcer is a common disease with increased prevalence in the aged population. Aged gastric mucosa has increased susceptibility to injury along with nonsteroidal anti-inflammatory drugs use due to impaired mucosal defense and decreased vasodilator release. We investigated whether l-arginine could protect against age-related gastric ulceration induced by indomethacin. Aged and adult male Wistar rats were administered sole and combined treatment of  l-arginine and Nω -nitro-l-arginine methyl ester ( l-NAME) before induction of gastric ulceration by indomethacin. The gastroprotective effect of  l-arginine was displayed only in adult rats with indomethacin-induced gastric ulceration, as evidenced by a significant decrease in ulcer index, oxidative stress parameters, and mucosal myeloperoxidase activity along with increased mucosal PGE2 levels. Interestingly, the mucosal gene expressions of NF-кB, iNOS, and COX-2 were significantly suppressed by  l-arginine pretreatment and aggregated upon pretreatment with  l-NAME in both adult and aged rats treated with indomethacin. In conclusion,  l-arginine protected the rats' gastric mucosa against indomethacin-induced gastric ulceration, possibly, at least in part, by enhancement of mucosal nitric oxide/PGE2 content along with suppressing gastric inflammation and oxidative stress. This study supposed that the gastroprotective effect of  l-arginine depends on aging, and even so, the adoption of a new approach to gastric ulcer treatment for the aged population is warranted.

The anti-inflammatory and analgesic activities of 2Br-Crebanine and Stephanine from Stephania yunnanenses H. S.Lo

Ethnopharmacological relevance: Crebanine (Cre) and Stephanine (Step) are isoquinoline aporphine-type alkaloids that are extracted from Stephania yunnanenses H. S. Lo. Plants of the Stephania genus are often used for treatment of stomach pain, abdominal pain, and rheumatoid arthritis. Both Cre and Step exhibit strong activities but are also associated with a certain level of toxicity, 10,11-dibrominecrebanine (2Br-Cre) is a bromine-modified derivative of Cre that we prepared and tested in order to reduce toxicity and enhance efficacy. Aim of this study: To investigate the anti-inflammatory and analgesic effects of 2Br-Cre and Step based on previous research findings and explore the specific biological mechanisms involved. Materials and methods: The anti-inflammatory and analgesic effects of 2Br-Cre and Step were investigated using a range of experimental models, including xylene-induced ear edema, carrageenan-induced pleurisy, carrageenan-induced paw edema, the hot-plate test, the naloxone antagonism test and the acetic acid writhing test. A model of chronic constriction injury (CCI) of the sciatic nerve was also established to investigate therapeutic effects. A RAW264.7 cell model was established using lipopolysaccharide (LPS) to estimate the effects of these compounds on cytokines levels. Results: 2Br-Cre and step significantly inhibited ear edema, paw edema and presented anti-inflammatory activity in the pleurisy model by inhibiting leukocyte migration and nitric oxide (NO) production, and by reducing the levels of PGE2. 2Br-Cre and Step significantly increased the pain threshold of mice subjected to heat stimulation; the effect was blocked by naloxone, thus suggesting that the analgesic effects of 2Br-Cre and Step were mediated by opioid receptors. 2Br-Cre and Step inhibited the frequency of writhing and prolonged the latency of writhing, and reduced the abnormal increase in the levels of BDNF in the serum and brain, thus alleviating the pain caused by CCI. In addition, 2Br-Cre and Step significantly inhibited the production of several inflammatory cytokines (IL-6, IL-1β and TNF-α) by LPS-induced RAW264.7 macrophages (p < .01). Conclusion: 2Br-Cre and Step exerted remarkable anti-inflammatory and analgesic effects. As a structural modification of Cre, 2Br-Cre retains the anti-inflammatory and analgesic activity of Cre but with better efficacy. Consequently, 2Br-Cre should be investigated further as a lead compound for analgesia.

Expression Profile of Cationic Amino Acid Transporters in Rats with Endotoxin-Induced Uveitis

Purpose. The transcellular arginine transportation via cationic amino acid transporter (CAT) is the rate-limiting step in nitric oxide (NO) synthesis, which is crucial in intraocular inflammation. In this study, CAT isoforms and inducible nitric oxide synthase (iNOS) expression was investigated in endotoxin-induced uveitis (EIU). Methods. EIU was induced in Lewis rats by lipopolysaccharide (LPS) injection. In the treatment group, the rats were injected intraperitoneally with the proteasome inhibitor bortezomib before EIU induction. After 24 hours, leukocyte quantification, NO measurement of the aqueous humor, and histopathological examination were evaluated. The expression of CAT isoforms and iNOS was determined by reverse transcription-polymerase chain reaction, western blotting, and immunofluorescence staining. Nuclear factor-kappa B (NF-κB) binding activity was evaluated by electrophoretic mobility shift assay. The mouse macrophage cell line RAW 264.7 was used to validate the in vivo findings. Results. LPS significantly stimulated iNOS, CAT-2A, and CAT-2B mRNA and protein expression but did not affect CAT-1 in EIU rats and RAW 264.7 cells. Bortezomib attenuated inflammation and inhibited iNOS, CAT-2A, and CAT-2B expression through NF-κB inhibition. Conclusions. CAT-2 and iNOS, but not CAT-1, are specifically involved in EIU. NF-κB is essential in the induction of CAT-2 and iNOS in EIU.

The crucial role of l-arginine in macrophage activation: What you need to know about it

Nowadays, it is well recognized that amino acids are powerful molecules responsible for regulatory control over fundamental cellular processes. However, our understanding of the signaling cascades involved in amino acid sensing in organisms, as well as signal initiation, is largely limited. This is also the case of semi-essential amino acid l-arginine, which has multiple metabolic fates, and it is considered as one of the most versatile amino acids. Recently, some new and important facts have been published considering the role of l-arginine in the regulation of inflammatory processes in several human and mouse models, mediated also via the regulation of macrophage activation. Therefore, this mini review focuses on the actual summarization of information about (i) l-arginine bioavailability in organism, (ii) l-arginine-dependent regulation of nitric oxide synthase expression and nitric oxide production, and importantly (iii) its role in the activation of intracellular signaling pathways and G-protein-coupled receptors in macrophages.

Enhancement of Inducible Nitric Oxide Synthase Activity by Low Molecular Weight Peptides Derived from Protamine: A Potential Therapy for Chronic Rhinosinusitis

Nitric oxide (NO) is a key immune defense agent that is produced from l-arginine in the airways by leukocytes and airway epithelial cells, primarily via inducible nitric oxide synthase (iNOS). Deficiencies in nasal NO levels have been associated with diseases such as primary ciliary dyskinesia and chronic rhinosinusitis. Herein, we demonstrate a proof-of-concept regarding a potential new therapeutic approach for such disorders. We show that arginine-rich low molecular weight peptides (LMWPs) derived from the FDA-approved protamine (obtained from salmon sperm) are effective at significantly raising NO production in both RAW 264.7 mouse macrophage and LA4 mouse epithelial cell lines. LMWP is produced using a stable, easily produced immobilized thermolysin gel column followed by size-exclusion purification. Monomeric l-arginine induces concentration-dependent increases in NO production in stimulated RAW 264.7 and LA4 cells, as measured by stable nitrite in the cell media. In stimulated RAW 264.7 cells, LMWP significantly increases iNOS expression and total NO production 12-24 h post-treatment compared to cells given equivalent levels of monomeric l-arginine. For stimulated LA4 cells, LMWPs are effective in significantly increasing NO production compared to equivalent l-arginine monomer concentrations over 24 h but do not substantially enhance iNOS expression. The use of the arginase inhibitor S-boronoethyl-l-cysteine in combination with LMWPs results in even higher NO production by stimulated RAW 264.7 cells and LA4 cells. Increases in NO due to LMWPs, compared to l-arginine, occur only after 4 h, which may be due to iNOS elevation rather than increased substrate availability.

The unique role of dietary L-arginine in the acceleration of peritoneal macrophage sensitivity to bacterial endotoxin

It is known that cells and organisms can indirectly "sense" changes in L-arginine availability via changes in the activity of various metabolic pathways. However, the mechanism(s) by which genes can be directly regulated by L-arginine in mammalian cells have not yet been elucidated. We investigated the effect of L-arginine in the in vivo model of peritoneal inflammation in mice and in vitro in RAW 264.7 macrophages. A detailed analysis of basic physiological functions and selected intracellular signaling cascades revealed that L-arginine is crucial for the acceleration of macrophage activation by bacterial lipopolysaccharide. L-arginine increased the production of reactive oxygen species, nitric oxide, release of Ca(2+), as well as inducible nitric oxide synthase expression. Interestingly, the effect of L-arginine on macrophage activation was dependent on the phosphorylation of mitogen-activated protein kinases and activity of phospholipase C. In RAW 264.7 cells, L-arginine was shown to modulate the response of macrophages toward lipopolysaccharide via the activation of G-protein-coupled receptors. According to our data, we concluded that L-arginine availability plays a key role in the initiation of intracellular signaling pathways that trigger the lipopolysaccharide-induced inflammatory responses in murine macrophages. Although macrophages are partially stimulated in the absence of extracellular L-arginine, the presence of this amino acid significantly accelerates the sensitivity of macrophages to bacterial endotoxin.

Control of mammalian gene expression by amino acids, especially glutamine

Molecular data rapidly accumulating on the regulation of gene expression by amino acids in mammalian cells highlight the large variety of mechanisms that are involved. Transcription factors, such as the basic-leucine zipper factors, activating transcription factors and CCAAT/enhancer-binding protein, as well as specific regulatory sequences, such as amino acid response element and nutrient-sensing response element, have been shown to mediate the inhibitory effect of some amino acids. Moreover, amino acids exert a wide range of effects via the activation of different signalling pathways and various transcription factors, and a number of cis elements distinct from amino acid response element/nutrient-sensing response element sequences were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine, the most abundant amino acid, which at appropriate concentrations enhances a great number of cell functions via the activation of various transcription factors. The glutamine-responsive genes and the transcription factors involved correspond tightly to the specific effects of the amino acid in the inflammatory response, cell proliferation, differentiation and survival, and metabolic functions. Indeed, in addition to the major role played by nuclear factor-kappaB in the anti-inflammatory action of glutamine, the stimulatory role of activating protein-1 and the inhibitory role of C/EBP homology binding protein in growth-promotion, and the role of c-myc in cell survival, many other transcription factors are also involved in the action of glutamine to regulate apoptosis and intermediary metabolism in different cell types and tissues. The signalling pathways leading to the activation of transcription factors suggest that several kinases are involved, particularly mitogen-activated protein kinases. In most cases, however, the precise pathways from the entrance of the amino acid into the cell to the activation of gene transcription remain elusive.

Thrombophilia, hypofibrinolysis, the eNOS T-786C polymorphism, and multifocal osteonecrosis

BACKGROUND

We examined the hypothesis that thrombophilia, hypofibrinolysis, and the endothelial nitric oxide synthase (eNOS) T-786C polymorphism are common, potentially treatable, and similar pathophysiologic causes of multifocal (three sites or more) and unifocal (single-site) osteonecrosis.

METHODS

We prospectively evaluated twenty-six consecutively referred adults with multifocal osteonecrosis, who included thirteen with idiopathic multifocal osteonecrosis and thirteen with secondary multifocal osteonecrosis (resulting from steroid therapy in ten and alcoholism in three). We compared these patients with race, sex, and age-matched normal control subjects and with patients with idiopathic unifocal and secondary unifocal osteonecrosis, respectively. Using polymerase chain reaction and serologic measures, we studied thrombophilic and hypofibrinolytic mutations and the eNOS T-786C polymorphism.

RESULTS

The total number of polymerase chain reaction and serologic thrombophilic-hypofibrinolytic abnormalities and the eNOS T-786C polymorphism did not differ between patients with idiopathic (p > 0.5) or secondary (p > 0.5) multifocal and unifocal osteonecrosis. The frequency of low free protein-S levels (<66%) in patients with secondary multifocal osteonecrosis (four of eleven patients) was higher than that in the control subjects (one of fifty-nine) (risk ratio = 21.5; 95% confidence interval, 2.6 to 174; p = 0.0016, Benjamini-Hochberg adjusted p [Bp] = 0.004). Factor-V Leiden heterozygosity was present in two of thirteen patients with secondary multifocal osteonecrosis compared with none of sixty-four control subjects (p = 0.027, Bp = 0.008). For eleven patients with secondary multifocal osteonecrosis, the eNOS T-786C polymorphism was present in nine of twenty-two alleles compared with eight of forty-four alleles in twenty-two normal control subjects (risk ratio = 2.3; 95% confidence interval, 1.0 to 5.0; p = 0.047, Bp = 0.016). The frequency of homocystinemia (>13.5 mumol/L) was higher in patients with idiopathic multifocal osteonecrosis (two of thirteen patients) than in normal controls (none of fifty-one) (p = 0.039, Bp = 0.004). A high level of factor VIII (>150%) was seen in four of eight patients with idiopathic multifocal osteonecrosis and in seven of forty-eight normal controls (risk ratio = 3.4; 95% confidence interval, 1.3 to 9.1; p = 0.04, Bp = 0.008). The eNOS T-786C mutant allele was present in seven of twelve alleles in the six patients with idiopathic multifocal osteonecrosis who were tested, compared with twenty-five of 108 alleles in fifty-four control subjects (risk ratio = 2.5; 95% confidence interval, 1.4 to 4.5; p = 0.015, Bp = 0.008).

CONCLUSIONS

Limited by the small numbers of patients with multifocal osteonecrosis, this exploratory study suggested that thrombophilia was associated with both idiopathic multifocal osteonecrosis and secondary multifocal osteonecrosis, as was the eNOS T-786C polymorphism. Multifocal and unifocal osteonecrosis are similarly associated with thrombophilia, hypofibrinolysis, and the eNOS T-786C polymorphism, which are potentially treatable pathophysiologic conditions, requiring further study.

Arginine homeostasis in allergic asthma

Allergic asthma is a chronic disease characterized by early and late asthmatic reactions, airway hyperresponsiveness, airway inflammation and airway remodelling. Changes in l-arginine homeostasis may contribute to all these features of asthma by decreased nitric oxide (NO) production and increased formation of peroxynitrite, polyamines and l-proline. Intracellular l-arginine levels are regulated by at least three distinct mechanisms: (i) cellular uptake by cationic amino acid (CAT) transporters, (ii) metabolism by NO-synthase (NOS) and arginase, and (iii) recycling from l-citrulline. Ex vivo studies using animal models of allergic asthma have indicated that attenuated l-arginine bioavailability to NOS causes deficiency of bronchodilating NO and increased production of procontractile peroxynitrite, which importantly contribute to allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction, respectively. Decreased cellular uptake of l-arginine, due to (eosinophil-derived) polycations inhibiting CATs, as well as increased consumption by increased arginase activity are major causes of substrate limitation to NOS. Increasing substrate availability to NOS by administration of l-arginine, l-citrulline, the polycation scavenger heparin, or an arginase inhibitor alleviates allergen-induced airway hyperresponsiveness by restoring the production of bronchodilating NO. In addition, reduced l-arginine levels may contribute to the airway inflammation associated with the development of airway hyperresponsiveness, which similarly may involve decreased NO synthesis and increased peroxynitrite formation. Increased arginase activity could also contribute to airway remodelling and persistent airway hyperresponsiveness in chronic asthma via increased synthesis of l-ornithine, the precursor of polyamines and l-proline. Drugs that increase the bioavailability of l-arginine in the airways - particularly arginase inhibitors - may have therapeutic potential in allergic asthma.